Salient Rotor Research Articles

Performance analysis of sandwich switched flux switching permanent magnet motor using modular rotor

Conventional flux-switching permanent magnet brushless machines (PMFSM) gained a lot of attraction due to their high torque densities, simple and robust rotor structure, and the permanent magnets and coils on the stator. The sandwich PMFSM machine has been proposed to improve the torque density of the machine in which two PM pieces are sandwiched in one stator pole to enhance the PMs usage efficiency. 2D finite element analysis (2DFEA) method is employed to compare the performance of sandwich PMFSM with salient rotor topology with that of sandwich PMFSM with modular rotor, in terms of flux linkage, flux distribution, flux strengthening, induced back EMF, cogging torque and average torque. From the results it is shown that the salient sandwich PMFSM and sandwich PMFSM modular rotor produces 9.28Nm and 6.7Nm, respectively.

Design of 6 slots/10 poles modular rotor sandwich switched flux switching permanent magnet motor

Conventional flux-switching permanent magnet brushless machines (PMFSM) gained a lot of attraction due to their high torque densities, simple and robust rotor structure, and the permanent magnets and coils on the stator. The sandwich PMFSM machine has been proposed to improve the torque density of the machine in which two PM pieces are sandwiched in one stator pole to enhance the PMs usage efficiency. 2D finite element analysis (2DFEA) method is employed to compare the performance of sandwich PMFSM with salient rotor topology with that of sandwich PMFSM with modular rotor, in terms of flux linkage, flux distribution, flux strengthening, induced back EMF, cogging torque and average torque. From the results it is shown that the salient sandwich PMFSM and sandwich PMFSM modular rotor produces 9.28Nm and 6.7Nm, respectively.

Maximum Torque Per Ampere Control Scheme Considering NI HTS Field Coil Behavior for Synchronous Motor With Salient Rotor Core

This paper presents characteristics analysis results of no-insulation (NI) high-temperature superconducting (HTS) motor with saliency according to motor control schemes. In case of a salient motor, for efficient operation, the commonly-known maximum torque per ampere (MTPA) control method is applied to generate the maximum torque at the given absolute value of stator current by using optimal dq-axes current pair ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$i^{r}_{ds}$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$i^{r}_{qs}$</tex-math></inline-formula> ). To figure out whether MTPA control is applicable for NI HTS motor, we applied three control schemes referred from conventional motor control method: (1) MTPA with constant parameters; (2) MTPA with variable parameters; and (3) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$i^{r}_{ds}=0$</tex-math></inline-formula> control. In addition, we proposed MTPA control with exponential function for suppressing radial leak current. The following key transient profiles of 500 kW NI HTS motor according to motor control schemes are presented: (1) dq-axes current; (2) field coil radial leak current; and (3) torque per ampere value.

Parameters estimation of non-saturated permanent magnet synchronous machines by aid of statistical analysis

The rotor position value is the most important parameter in synchronous machines. In this paper, a MATLAB model of high-resolution rotor position determination at zero speed, without any position sensor, is presented for a non-saturated permanent magnet motor. The motor current and voltage responses for two short pulses were employed to form address lines for memory cells whose contents represent the exact rotor position. The proposed model presents rotor position at 1o resolution and works with salient rotor poles. It could be modified to obtain the results for non-salient poles. The model needs only two current sensors and does not require any special technique for magnet polarity detection. This method was tested successfully for a two-poles machine and it could be applicable to any number of poles.

Continuous Rotor Position Estimation for Flux Modulated Doubly Salient Reluctance Motor Drives Based on Back EMF Harmonics

DC-biased sinusoidal current excited flux modulated doubly-salient reluctance motor (FMDRM) drives are developed to reduce the torque ripple and vibration of doubly-salient reluctance motors (DRMs). Conventionally, because of the discontinuous quasi-square current excitation, the rotor position of DRMs is estimated by the combination of piecewise estimation of phase angle information for each phase, where the continuous position estimation for the novel FMDRM drives cannot be realized. To solve this issue, this paper proposes a continuous rotor position estimation strategy for FMDRM drives based on back electromotive force (back-EMF) harmonic characteristics. Firstly, the back-EMF harmonics caused by the rotor saliency and their relationship with the rotor position are analyzed in detail. Then, the corresponding harmonic current regulator and quadrature signal generator are investigated to achieve harmonic current suppression and obtain the quadrature harmonic back-EMF components in the rotating reference frame for rotor position estimation simultaneously. Furthermore, a virtual-inductance-based method is developed to calibrate the phase angle offset between the estimated and actual rotor positions. With the proposed scheme, accurate continuous rotor position estimation can be achieved without any additional hardware. Experimental validations are presented on a three-phase 12&#x002F;8 FMDRM prototype to verify the accuracy of the proposed rotor position estimation scheme.

Magnetic equivalent circuit and finite element modelling of anisotropic rotor axial flux permanent magnet synchronous motors with fractional slot distributed winding

AbstractAxial flux motors have been in the focus of many research work due to their promising properties when compared to conventional radial flux machines. Axial flux permanent magnet synchronous motors (AFPMSM) studied in the literature were mostly limited to surface‐mounted permanent magnet machines (SPMSM), excluding only a few studies about axial flux internal permanent magnet (AFIPM) or permanent magnet‐assisted synchronous reluctance (AFPMaSynRM) machines. Since numerous rotor topologies have been proposed and investigated in case of radial flux motors, analogous design methodologies can be developed in case of axial flux motors with rotor saliency. The parametrisation and modelling of a magnetically anisotropic rotor axial flux motor are presented. This approach is described generally and the method is applied to an example motor geometry. The results were validated by FEA (Finite Element Analysis), using the 2D multi‐slice and 3D modelling approaches. The modelling error was calculated and the analytical and numerical methods were compared. It was found that the proposed model was suitable for calculating important parameters of the anisotropic rotor axial flux permanent magnet synchronous motor (AnR‐AFPMSM) during the design process.

Kriging-Assisted Multiobjective Optimization of Embedded Magnetic Encoder in PM Synchronous Machines

The embedded magnetic encoder (EME), located in stator slot of permanent magnet (PM) synchronous machines (PMSMs), monitors the PM flux-density in the cavity and feedback the rotor angle for vector control. To reduce the total harmonic distortion (THD) of flux-density and improve the angle estimation accuracy, the topology optimization of PMSMs can be carried out. However, as THD is set as the only objective during optimization, the other characteristics, e.g., back electromotive-force (back-EMF) due to PMs, and winding inductance of PMSMs will uncontrollably change. Hence, a systemic design optimization of PMSM combined with EME is necessary. Different from the traditional multi-objective optimization of electric machines based on the time-consuming finite element analysis (FEA), in this paper a Kriging-assisted surrogate model is proposed to replace FEA during optimization, achieving time saving and high prediction accuracy simultaneously. The decision variables are carefully selected. e.g., a Cosine function reshaping method is proposed and proper linear Hall installation position is analyzed. In the preliminary optimization, the Pareto front with minimum THD and maximum rotor saliency is obtained. Further, by modifying the THD objective with retaining the third harmonic component, the THD becomes lower and rotor saliency is increased in the optimal case. Finally, three different rotors are manufactured to verify the effectiveness of proposed reshaping method and improved optimization strategy.

Performance Analysis and Comparison for Various Excitation Source Salient Rotor with Modular Rotor Permanent Magnet of Flux Switching Machine

Performance Analysis and Comparison for Various Excitation Source Salient Rotor with Modular Rotor Permanent Magnet of Flux Switching Machine

High efficiency flux switching motor

Flux switching motor (FSM) with field excitation is permanent magnet free and attractive for many industrial and domestic applications. However, design with the conventional trapezoidal stator slot has low efficiency and always been a challenge in the state of the art. Further, the finite element analysis (FEA) method for the electromagnetic performance investigation is a powerful tool, but, it has high computational time, computational complexity and drive storage. To address the concern of low efficiency, in this paper, a new single phase 8slots–6poles electrically excited (EE) FSM design with the rectangular stator slot (RSS), salient rotor and non-overlapped windings for pedestal fan applications is been proposed. The proposed RSS EEFSM design is analyzed analytically and the analytical results are validated by FEA method. Finally, experimental test of the proposed EEFSM prototype is performed. The measured results are in a good agreement with the calculated results. Moreover, the proposed RSS EEFSM has higher efficiency as compared to the conventional design.

Quantitative Comparison on Permanent-Magnet Vernier Machines With Improved Flux Modulation Effect for Automatic Guided Vehicles

In this paper, the interior permanent-magnet vernier (PMV) machines and the conventional PMV machine are quantitatively compared regarding the requirements for electric automatic guided vehicles (AGV). The key feature of the interior PMV machines is to place the middle iron pole sandwiched by PMs in the slots between the salient rotor poles. As a result, three types of interior PMV machines with different PM arrangements, namely two V-type PMV (V-PMV) and one U-type PMV (U-PMV) machines, are developed. Due to the improved flux modulation effect, the V-PMV and U-PMV machines can respectively provide over 20% and 30% higher torque density than the conventional PMV counterpart, under a high power factor level of 0.86. The working principle is illustrated based on the field modulation theory. A comparative study among the conventional PMV and interior PMV machines is conducted in terms of electromagnetic performances and dynamic responses, after performing global optimization of design parameters. Finally, a prototype is manufactured and tested for experimental validations.

Hybrid winding function method for inductance analysis of a line start synchronous reluctance machine

In recent years, there has been renewed interest in line-start synchronous reluctance machines (LSSRMs) due to their simple construction, magnet-free rotor, and low cost. To improve control performance, design optimization, and fault diagnostic analysis of these machines, it requires accurate estimation of their electromagnetic characteristics using detailed and time-consuming finite element analyses (FEAs). In this paper, inductances and electromagnetic torque of the LSSRM were calculated using the combination of winding function analysis and conformal mapping instead of FEA. The hybrid approach can be applied to the prediction of motor behavior, taking into account all space harmonics of the air-gap permeance without any restriction on the rotor saliencies and topologies. The influence of the core saturation, stator slots, and rotor bars were also considered. The results obtained by simulations were compared with FEA in terms of accuracy and computational time.

Hybrid Position Estimation Strategy With a Smooth Transition for IPMSM Sensorless Drives in the Wide Speed Range

In this article, an innovative hybrid position estimation strategy along with the minimum voltage vector injection (MVVI) method and the back electromotive force (back EMF) based method is proposed for interior permanent magnet synchronous motors (IPMSMs) in full-speed regions. At zero- and low-speed, the MVVI method based on rotor saliency is used for position estimation; the inverter voltage error is counteracted in estimating the rotor position, minimizing the inverter nonlinearity effect without introducing external errors. For IPMSMs at the initial state, this article proposes to utilize the high frequency <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current excited by injection voltage itself directly for the polarity detection. The position estimation at low-speed based on the MVVI method has such advantages as no requirement for filters, fast convergence, and reliability of magnetic polarity detection. In addition, a smooth transition blends the MVVI method and the back EMF based method is proposed, and a compensation term based on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis feedback current is added on the error of both the reference and feedback speed to reject the load-disturbance within the low speed and transition region. Experimental results show that the proposed hybrid sensorless control strategy exhibits excellent performance in the full speed range for both steady-state and dynamic operations.

Electromagnetic Analysis for Interior Permanent-Magnet Machine Using Hybrid Subdomain Model

This paper proposed a hybrid subdomain model (HSM) for calculating the magnetic field distribution of interior permanent-magnet (IPM) machine accounting for slotting effect, rotor saliency, and iron nonlinearity. In the constant permeability region, i.e., slots, slot-opening, and air-gap, three subdomains are introduced to represent their magnetic field. By applying the subdomains interface conditions and nonlinear boundary conditions, the analytical air-gap field solution can be obtained based on the governing Laplace and Poisson equation. For the iron region, the magnetic reluctance network (MRN) is proposed to account for rotor saliency iron and nonlinearity. The magnetic voltage source is introduced to represent the permanent-magnet (PM) while the air-gap flux source is used to replace the air-gap reluctance network, which is the key to guarantee the computational efficiency and high accuracy. The electromagnetic performances of both flat-shaped and V-shaped IPM machines are investigated to show the advantages of different IPM machine topologies analytically. The HSM predictions for both IPM machines are validated by finite-element (FE) analysis and experimental results.

Reluctance Synchronous and Flux-Modulation Machines Designs: Recent Progress

Electric machines provide the conversion of mechanical energy to electrical energy (in the generating mode) and vice versa (in the motoring mode), via magnetic energy storage in their airgap (mainly) and in their permanent magnets (PMs) (if any). They are crucial in electric energy conversion and processing and for motion (torque, speed, and position) control in all industries, for better productivity, energy savings, and less harm to environment. Traveling field electric machines are still standard as synchronous and induction machines. The former (synchronous) need dc rotor excitation, or PMs or magnetically salient rotor to create a-fixed-to-rotor traveling field while the latter (induction) implies a cage (or wound) rotor winding. The average torque is nonzero as stator and rotor traveling fields are at standstill with each other. In an effort to take advantage of the variable reluctance concept in producing nonzero magnetic co-energy (and torque) in the machine versus variation of rotor position, better reluctance synchronous machines (RSMs) (line-start or inverter-fed) in terms of efficiency <inline-formula> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> power factor, torque density, and costs without and with assisting PMs have been introduced lately. High magnetic saliency is implicit and requires a high ratio of pole pitch to airgap and a distributed ac stator winding, in the hope to meet the IEC 4, 5 standards of efficiency. On the other hand, better magnetic materials (with lower core losses) and higher fundamental frequency provided by pulsewidth modulation (PWM) static power converter (including silicon carbide (SiC) arrival) up to 1 kHz, in general, and the high price (and scarcity) of high energy PMs have triggered formidable Research and Development worldwide efforts to investigate many machine topologies without and with PMs (mainly ferrites or bonded NdFeB of lower cost), with mainly concentrated ac windings based on the principle of &#x201C;flux-modulation (F-M)&#x201D; provided by variable reluctance (magnetic anisotropy) concept. This article aims to summarize recent progress in reluctance electric machines, without and with PM assistance of synchronous and &#x201C;F-M&#x201D; types in terms of topologies, modeling, design, control, and merits and demerits based on comprehensive-technical and economic performance indexes.

Decoupling control of a bearingless switched reluctance motor with hybrid-rotor

In order to solve the coupling between torque and suspended force of the traditional bearingless switched reluctance motor (BSRM), a bearingless switched reluctance motor with hybrid-rotor (HBSRM) is proposed in this paper. The HBSRM discussed in the paper has a twelve-pole stator and an eight-pole hybrid-rotor composed of a cylindrical rotor and a salient rotor. The magnetic pulling force between cylindrical rotor and stator is used to independently levitate the shaft, and that between salient rotor and stator is used to separately rotate the rotor. So, the HBSRM not only breaks the restriction of the effective output region between torque and suspended force in the traditional BSRM, but also facilitates the decoupling algorithm design and simplifies the levitation control of this bearingless motor. Firstly, the topology, operating mechanism and mathematical model of the proposed HBSRM are introduced respectively. Then the no-load decoupling control and torque ripple of the traditional BSRM and HBSRM are compared. Moreover, the load decoupling control characteristics of HBSRM are presented and verified by simulation analysis.

A Novel Multi-Excitation-Tooth Nonoverlapping Stator Wound Field Synchronous Machine With Salient Rotor

In this paper, based on the conventional nonoverlapping stator wound field synchronous (N-SWFS) machine, a novel multi-excitation-tooth N-SWFS (MN-SWFS) machine is firstly proposed by changing winding configurations and the excitation-teeth shape. The electromagnetic performance of four optimized MN-SWFS machines sharing the same 12-stator-teeth but different rotor-teeth numbers, namely 12/10, 12/11, 12/13, and 12/14, is compared by finite element analysis (FEA). The corresponding simulation results show that 12/10 and 12/14 are the optimal stator-teeth/rotor-teeth combinations due to much smaller back electromotive force (back-EMF) THD and torque ripple (<i>T_rip</i>). Finally, a series of comparative studies are carried out on the proposed MN-SWFS machines and the conventional N-SWFS machines. The comparative results validate that the proposed 12/10 and 12/14 MN-SWFS machines exhibit better electromagnetic performance than the conventional 12/11 and 12/13 N-SWFS machines, such as higher fundamental back-EMF amplitude and greater torque output capability, though their cogging torque (<i>T_cog</i>) and torque ripple are slightly higher, and the torque anti-saturation ability is slightly weaker.

Analysis of the Saliency Ratio Effect on the Output Torque and the System Efficiency in IPM Drives

Permanent magnet synchronous motors (PMSM) can be classified into two groups based on the rotor saliency structure as surface mounted permanent magnet synchronous motors (SPM) and interior mounted permanent magnet synchronous motors (IPM). Saliency ratio is defined as the ratio of q- axis inductance to d- axis inductance. While SPMs with the same d- and q- axis inductance values have the capacity to generate only the magnet-based torque IPMs are salient machines and they also produce reluctance torque due to the difference in inductances. This study analyses the influence of the saliency ratio on the drive system efficiency and the torque production capability of salient machines. First, efficient torque control systems have been implemented and successfully achieved for two identical IPMs with only difference in saliency ratios. Then, tests were carried out on the drive systems for two IPMs. It has been validated by extensive simulation results that the torque production capacity and the efficiency of the drive system can be increased considerably if the saliency ratio can be increased at the stage of machine design.

FE-Aided Synchronization Analysis of Line-Start Synchronous Reluctance Motors

Since line-start synchronous permanent magnet motors (LSPMs) entered the market, they have attracted research interest toward counterpart induction motors of low power-ratings. This paper reports an investigation of line-start synchronous reluctance motors (LS-SynRMs). LS-SynRMs has not been investigated as much as LSPMs have. A motor needs to maximize rotor saliency to achieve high efficiency and a high power-factor. This results in complicated rotor geometry because the rotor cage and multiple flux barriers share the same rotor space. This paper provides an approximate method based on steady state torque analysis by which to estimate the critical inertia of a LS-SynRM. A finite element analysis (FEA)-aided analytical approach to the approximation of steady state torque is proposed to replace the more typical approach based on equivalent circuit parameters. The critical inertia resulting from the proposed method is compared to the results obtained using the FEA.

Modeling and analysis of variable reluctance resolver using magnetic equivalent circuit

Purpose The purpose of this paper is to propose a saturable model based on the magnetic equivalent circuit (MEC) for evaluating the electromagnetic performance of the variable area resolver. Design/methodology/approach The equivalent circuit is developed where three different reluctance types are used to calculate permeances based on geometrical approximations. The proposed model typically has two types of equations, including the magnetic and electrical equations. The magnetic and electrical equations are related to the resolver core and the windings, respectively. Applying the well-known trapezoidal method, the magnetic and electrical equations can be simultaneously solved. A nonlinearity of the magnetic equations, the algebraic equations system, which is obtained from Kirchhoff’s laws, should be solved by the Newton-Raphson technique in each step-time. Findings The flexible MEC model, in which the number of flux tubes in different parts of the resolver can be arbitrarily selected, is proposed to analyze the variable reluctance resolver. Besides, the design parameters such as geometrical dimensions, windings arrangement and a number of the rotor saliencies can be chosen as desired. To consider the effect of time harmonics, a new nonlinear function is used for the core magnetization. Furthermore, different winding layouts can be implemented in the model to take space harmonics into account. The model obtained results are compared with the finite element method in terms of accuracy and simulation time. Originality/value Generally, the accuracy of the predictions in the MEC method is dependent on the number of flux tubes; therefore, the flexibility of the proposed MEC model in its capability to choose the desired number of flux paths is the advantage of this work. Moreover, the proposed model can analyze both wound and saliency rotor resolvers by changing the design parameters.

Coil Number Impact on Performance of 4-Phase Low Speed Toothed Doubly Salient Permanent Magnet Motors

The low speed toothed doubly salient permanent-magnet (TDSPM) machine is an interesting candidate motor for electric ship applications because, of its high torque output, maintenance-free operation and flexible working modes, which gives the opportunity to increase system’s reliability, and decrease the system size, weight and noise which are key features for naval applications. However, particularly in the 3-phase configuration, the stator and rotor saliency of these machines leads to a high level of torque ripple. To overcome these drawbacks, the use of polyphase machines (with a number of phases greater than three) can be a relevant solution. In this paper, an optimal design of two kind of novel 4-phase motors is performed in order to fulfil the specifications of a high power naval ship propulsion. The designs aim to maximize the torque to mass ratio. The motors’ performances are directly linked to their structural parameters, so, the impact of the coil number in terms of mean torque, torque ripple, energy ratio values, and efficiency is also presented and analysed. The design of these two electromagnetic structures, as well as the determination of their electromagnetic performances, are carried out using a particle swarm optimization algorithm (PSO) with taking into account thermal constraint. The performance of the proposed machine in terms of mean torque, torque ripple, energy ratio, and efficiency values is presented and analysed. The results obtained reveal that the TDSPM machines with four poles/phase are good candidates to meet the requirements of high power direct-drive ship propulsion system.